Solid-state fluorescent pH sensors based on pyrimidine/purine-cored covalent organic framework

Fluorescent covalent organic frameworks have been increasingly used as chemical sensors due to their inherent outstanding nature. Here we report two cases of β-ketoenamine typed fluorescent COFs, pyrimidine-cored covalent organic framework (TpApy-COF) and purine-cored covalent organic framework (TpApu-COF). The emission intensities of TpApy-COF and TpApu-COF in aqueous dispersion descend gradually with the ascending of pH value in the range of from 1 to 13. The reversible fluorescence transformation along with the pH change indicates the favorable reusabilities of TpApy-COF and TpApu-COF. The successful assembly of fluorescent liquid glue and fluorescent crayon, as well as their fluorescent turn on and turn off sensing of HCl and NH 3 , suggest positive practicability and processability. The formation and disintegration of extra intramolecular H-bonding during protonation and deprotonation play crucial roles in the reversible fluorescence switching.